Ford M J, Bickle Q D, Taylor M G
Parasitology. 1984 Oct;89 ( Pt 2):327-44. doi: 10.1017/s0031182000001347.
In PVG rats a single immunizing infection with Schistosoma mansoni cercariae exposed to 0, 5, 10 or 20 krad. gamma radiation failed to induce more than minimal resistance (17-29%) to challenge 4 weeks later, whereas 4 immunizations with 20 krad.-irradiated cercariae, over several months, induced substantial resistance (75%). In contrast, significant protection was induced in Fischer rats by a single immunization with unirradiated cercariae or cercariae irradiated with up to 80 krad. Comparable resistance was induced by unirradiated and by 2, 5 and 20 krad.-irradiated cercariae (67-74%) and lower levels by 10, 40 and 80 krad.-irradiated infections (57, 48 and 33%, respectively). Although the resistance induced by a single dose of 1000 20 krad.-irradiated cercariae could be boosted by a second (88%), further immunizations failed to enhance this resistance. Also, increasing the number of immunizing cercariae in single or multiple vaccinations from 1000 to 3000 failed to increase the resistance. While the resistance induced by 20 krad.-irradiated cercariae persisted undiminished for at least 25 weeks (67%), the resistance induced by normal cercariae declined to insignificant levels by 25 weeks (21%). Comparison of the migration and survival of unirradiated and of 20 and 40 krad.-irradiated cercariae revealed dramatic differences in their fate: parasites exposed to 40 krad. remained in the skin, while the majority of 20 krad.-irradiated parasites died in the lungs after a sojourn of at least 14 days. Thus, although skin schistosomula alone could induce significant protection, optimal resistance was induced only by parasites which migrated to the lungs or beyond. The immunizing potential of these older parasites was investigated by exposing rats to lung- and liver-stage larvae injected into the tail and mesenteric veins, respectively. Irradiated 4-day lung schistosomula induced comparable resistance (79%) to that induced by a complete unattenuated cercarial infection (78%), whereas less resistance was induced by irradiated and unirradiated 11-day-old liver worms (30 and 27%) and by 25-day-old pre-adult worms (48%).
在PVG大鼠中，用暴露于0、5、10或20千拉德γ射线的曼氏血吸虫尾蚴进行单次免疫感染，4周后对攻击的抵抗力不超过最低限度（17 - 29%），而在几个月内用20千拉德辐照的尾蚴进行4次免疫，则诱导出显著的抵抗力（75%）。相比之下，用未辐照的尾蚴或辐照剂量高达80千拉德的尾蚴对Fischer大鼠进行单次免疫，可诱导出显著的保护作用。未辐照的以及2、5和20千拉德辐照的尾蚴诱导出相当的抵抗力（67 - 74%），而10、40和80千拉德辐照感染诱导的抵抗力较低（分别为57%、48%和33%）。虽然单次剂量的1000条20千拉德辐照的尾蚴诱导的抵抗力可通过第二次免疫增强（88%），但进一步免疫未能增强这种抵抗力。此外，在单次或多次疫苗接种中将免疫尾蚴的数量从1000条增加到3000条，并未增加抵抗力。虽然20千拉德辐照的尾蚴诱导的抵抗力至少25周内保持不变（67%），但正常尾蚴诱导的抵抗力到25周时降至微不足道的水平（21%）。对未辐照的以及20和40千拉德辐照的尾蚴的迁移和存活情况进行比较，发现它们的命运存在显著差异：暴露于40千拉德的寄生虫留在皮肤中，而大多数20千拉德辐照的寄生虫在肺部停留至少14天后死亡。因此，虽然仅皮肤期血吸虫幼虫就能诱导出显著的保护作用，但只有迁移到肺部或更远部位的寄生虫才能诱导出最佳抵抗力。通过分别将大鼠暴露于注入尾静脉和肠系膜静脉的肺期和肝期幼虫，研究了这些较老寄生虫的免疫潜力。辐照4天的肺期血吸虫幼虫诱导出的抵抗力（79%）与完全未减毒的尾蚴感染诱导的抵抗力（78%）相当，而辐照和未辐照的11日龄肝期虫体（3个和27%）以及25日龄的成虫前期虫体（48%）诱导的抵抗力较低。
